000
WTPA41 PHFO 310832
TCDCP1
TROPICAL STORM LANA DISCUSSION NUMBER 4
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP062009
ISSUED BY NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1100 PM HST THU JUL 30 2009
LANE HAS DEVELOPED A CENTRAL CONVECTIVE FEATURE THIS EVENING...WITH
03Z SSM/IS DATA SUGGESTING GOOD CONVECTIVE BANDING NEAR THE CENTER.
SINCE THEN...THE CONVECTIVE TOPS HAVE WARMED SOMEWHAT. AMSU
INTENSITY ESTIMATES NEAR 03Z WERE 50-60 KT...WHILE QUIKSCAT DATA
NEAR 04Z SHOWED 40-45 KT WINDS NORTHEAST OF THE CENTER. THE
SATELLITE INTENSITY ESTIMATES ARE 45 KT FROM TAFB AND 55 KT FROM
SAB. THE INITIAL INTENSITY IS THE ROUGH AVERAGE OF THESE
VALUES...50 KT.
THE INITIAL MOTION IS 285/17. A LOW/MID-LEVEL RIDGE LOCATED TO THE
NORTH OF LANA SHOULD PROVIDE THE STEERING DURING THE NEXT SEVERAL
DAYS AS A LARGE UPPER-LEVEL LOW SEEN IN WATER VAPOR IMAGERY MOVES
WESTWARD FROM THE HAWAIIAN ISLANDS. THE TRACK GUIDANCE SUGGESTS
THIS PATTERN SHOULD STEER LANA GENERALLY WESTWARD TO WEST-
NORTHWESTWARD SOUTH OF HAWAII THROUGH THE FORECAST PERIOD.
OVERALL...THE GUIDANCE IS TIGHTLY CLUSTERED EXCEPT FOR THE OUTLYING
BAMD AND BAMM...WHICH FORECAST LANA TO MOVE NORTHWESTWARD THROUGH
OR NEAR THE HAWAIIAN ISLANDS. THE GUIDANCE ENVELOPE HAS AGAIN
SHIFTED A LITTLE TO THE NORTH...SO THE NEW TRACK WILL BE NUDGED A
LITTLE NORTH OF THE PREVIOUS FORECAST. THE NEW TRACK IS ALONG THE
SOUTH SIDE OF THE GUIDANCE ENVELOPE IN BEST AGREEMENT WITH THE GFS
AND GFDL MODELS.
LANA IS CURRENTLY IN AN ENVIRONMENT OF LIGHT SOUTHERLY WIND SHEAR
WITH FAIR TO GOOD CIRRUS OUTFLOW. THE LARGE-SCALE MODELS FORECAST
THAT LANA WILL GRADUALLY MOVE CLOSER TO THE STRONG SOUTHERLY AND
SOUTHWESTERLY FLOW ASSOCIATED WITH THE UPPER-LEVEL LOW...WHICH
SHOULD CAUSE A SIGNIFICANT INCREASE IN VERTICAL WIND SHEAR AFTER
24-36 HR. THE INTENSITY GUIDANCE CALLS FOR THE STORM TO REACH A
PEAK INTENSITY OF 60-65 KT BEFORE THE SHEAR INCREASES...AND THE NEW
INTENSITY FORECAST CALLS FOR A 65 KT PEAK INTENSITY IN 24 HR IN
AGREEMENT WITH THE PREVIOUS FORECAST. AFTER THAT...LANA SHOULD
STEADILY WEAKEN DUE TO THE SHEAR. THE UKMET AND ECMWF MODELS SHOW
VERY STRONG SHEAR BY 72 HR...AND IF THEY ARE CORRECT LANA COULD
WEAKEN FASTER THEN CURRENTLY FORECAST.
FORECAST POSITIONS AND MAX WINDS
INITIAL 31/0900Z 13.3N 144.6W 50 KT
12HR VT 31/1800Z 13.6N 147.0W 60 KT
24HR VT 01/0600Z 14.1N 149.8W 65 KT
36HR VT 01/1800Z 14.6N 152.7W 65 KT
48HR VT 02/0600Z 15.1N 155.5W 60 KT
72HR VT 03/0600Z 16.0N 161.0W 45 KT
96HR VT 04/0600Z 17.0N 166.5W 30 KT
120HR VT 05/0600Z 17.5N 172.0W 25 KT...REMNANT LOW
$$
FORECASTER BEVEN